The invention relates generally to an electrostatic clutch. More specifically, the invention relates to a lightweight and high power density electrostatic clutch that can be incorporated into robotic systems, including exoskeletons and wearable devices, among other uses.
Clutches have many uses in mechanical systems, often being used to improve the functionality of springs and actuators. However, existing clutch systems suffer several drawbacks when used in mobile applications, such as robotics. For example, electromagnetic clutches feature fast activation and moderate torque density, but require continuous electrical power to stay active. Magnetorheological clutches produce large torques, but are heavy and also require continuous power to remain active. Because of the power requirements, both of these systems require large batteries or tethered electrical connections. Mechanical latches require no energy to stay active, but only engage and disengage under special conditions.
The problems associated with traditional clutches are particularly pronounced in wearable robotic systems, such as exoskeletons. Assistive robotic exoskeletons have shown positive impacts for people in a variety of applications, including physical performance augmentation and medical treatment. One challenge associated with autonomy is the metabolic cost associated with carrying the combined weight of the exoskeleton structure, energy storage, actuators, and electronics. Batteries in particular account for a significant portion of the weight of many devices, especially in devices with clutches that require constant power. In addition to the weight of batteries, significant weight penalties are experienced with commercially available actuators, such as motors and pneumatic actuators.
Walking on level ground is an example of an application where traditional actuators and motors are not well suited for robotic applications. Walking on level ground at a constant speed requires very little energy input since the potential and kinetic energies of the moving body do not change on average. However, approximately equal amounts of positive and negative work are performed by the legs during a walking cycle. Both the positive and negative work require energy, since the negative work cannot be stored and reused as an input for the positive work.
If an actuator could absorb and return mechanical energy, the total energy consumption of the system could be reduced. Ideally, energy recycling could supply all needed positive work by absorbing and reusing negative work movements. As an added benefit, using a device to absorb energy from negative work movements would reduce the metabolic cost of a human wearing a robotic device because muscles require energy to perform negative work.
Lightweight, low-power, and electrically controllable clutches would allow greater performance of many robotic systems. Improved clutches could be incorporated into actuators to substantially improve the actuator's energy demands. Therefore a need exists for a clutch that does not exhibit any of the shortcomings of traditional clutches.